Molecular epidemiology and antimicrobial resistance of Corynebacterium diphtheriae and Corynebacterium ulcerans strains isolated in the UK between 2004-2017

The genus Corynebacterium includes three potentially toxigenic species, C. diphtheriae, C. ulcerans and C. pseudotuberculosis, capable of causing diphtheria, a severe disease in humans. The aims of this study were to undertake Multi-Locus Sequence Typing (MLST) on a panel of both toxigenic and non-toxigenic C. diphtheriae and C. ulcerans strains (20 toxigenic and29 non-toxigenic C. diphtheriae, 17 toxigenic and 14 non-toxigenic C. ulcerans) isolated in the UK between 2004 and 2017, and use these results to determine the molecular epidemiology within the UK. Antibiotic sensitivity testing was also undertaken (20 toxigenic and 88 non-toxigenic C. diphtheriae, 17 toxigenic and 14 non-toxigenic C. ulcerans) and their profiles compared. The MLST results showed that C. diphtheriae and C. ulcerans isolates formed two distinct genetic populations and that C. diphtheriae isolates with intermediate penicillin resistance demonstrated sequence types which were genetically related. The results also showed that ST32 was most prevalent (31%, 9/29 isolates) amongst non-toxigenic C. diphtheriae. Non-toxigenic C. ulcerans isolates demonstrating intermediate penicillin resistance formed distinct genetic populations and appeared distantly related or unrelated. There were 75 % (15 isolates) of toxigenic C. diphtheriae isolates, 35 % (6 isolates) of toxigenic C. ulcerans isolates, 30 % (26 isolates) non-toxigenic C. diphtheriae and 43 % (6 isolates) of non-toxigenic C. ulcerans which demonstrated intermediate penicillin resistance. Linezolid and vancomycin were the only antibiotics which demonstrated 100 % sensitive profiles for all isolate groups. These data will help inform public health guidance and management of corynebacteria infections caused by these species.